Various types of longitudinally, or axially slit pressure cylinders have been proposed. The sealing strip may be a flexible tape or ribbon which engages a sealing surface formed in the inner wall of the cylinder. At the outer wall of the cylinder, the sealing strip is carried over and/or through an opening in the power transfer element--which may be generally U-shaped. In one form, and to stiffen the cylinder, the flexible sealing strip, which is lifted off the sealing surface in regions opposite the piston is covered by a flexible cover strip or tape. Releasable connection elements are provided, retaining the cover strip or tape to the sealing strip which are released to permit separation as the piston travels in the separating direction, and to be reattached behind the piston to form a sealing and cover strip.
In a pressure cylinder with these characteristics, known from U.S. Pat. No. 4,664,020, to which German Patent No. 31 24 878 corresponds, the sealing strip and the cover strip are respectively formed as flexible plastic profiled strips, the connecting parts of which consist of a longitudinal ridge formed on one of the strips and of a longitudinal slit developed in the other strip which is arranged to receive the ridge. Although this results in a perfect sealing of the elongated axial slit on both sides of the force transfer element, the maximum amount of the pressure of the pressure means with which the interior of the cylinder structure can be charged is limited. This is because, when a certain maximum pressure is exceeded, there is a danger of the flexible plastic sealing strip being pressed into the axial slit by the pressure means while undergoing plastic deformation and thus losing its sealing ability. For this reason, the known cylinder can only be used in a lower pressure region such as is typical for a pneumatic cylinder.
A similar pressure cylinder with axially slit cylinder is known from U.S. Pat. No. 4,373,427, where the elongated axial slit is also sealingly closed by a sealing strip extending on the inside of the cylinder structure and a cover strip disposed on the exterior of the cylinder structure on both sides of the force transfer element. Both the sealing strip and the cover strip are two-layered; a plastic or rubber strip made of elastically deformable material and having a greater thickness is deposited on a thin ferritic steel strip. Both the sealing strip as well as the cover strip have a generally trapezoidal cross section, while correspondingly inclined surfaces are provided as sealing surfaces in the wall of the cylinder structure on both sides of the elongated axial slit, with which the elastomeric material layer of the respective strip cooperates sealingly. Especially in order to hold the sealing strip in the elongated axial slit, permanent magnets are disposed in the area of the edges of the elongated axial slit in the cylinder structure, the magnetic force lines of which can close via the ferritic steel strip of the sealing as well as the cover strip and thereby exert a magnetic drawing force on these strips.
Since the flat even steel strip on the side of the sealing strip oriented towards the piston is openly disposed, flat regions must be provided on the piston and on the piston seal gaskets, otherwise cylindrical in cross section, in the area opposite the sealing strip, which are undesirable and can lead to sealing problems in the piston sealing gaskets. Furthermore, the sealing effect obtainable from the elastomeric layer of the two-layered sealing strip is limited because the inner metal strip rests on the inclined sealing surfaces and thereby prevents the further pressing of the elastomeric parts on the sealing surfaces. To prevent this, the cylinder structure must be manufactured to relatively close tolerances in the area of its sealing surfaces and in the dimensions of its elongated axial slit, which is expensive and requires added effort.